Polyaxial bone anchoring device and system of an instrument and a polyaxial bone anchoring device

ABSTRACT

A bone anchoring device includes a receiving part having a first end with an end surface, a second end, a recess at the first end for receiving a rod, and a flexible head receiving portion at the second end for pivotably holding a head of a bone anchoring element, and a clamping ring positionable around the head receiving portion and movable from a first position where the head is pivotable relative to the receiving part, to a second position where the clamping ring exerts a radial force onto the head receiving portion to lock the head. The receiving part further includes a first engagement structure at or adjacent the end surface extending radially outwardly from an outer surface of the receiving part, such that a width of the receiving part including the first engagement structure is at least as wide as a maximum width of the clamping ring.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No. 15/669,541, filed Aug. 4, 2017, which claims the benefit of U.S. Provisional Patent Application Ser. No. 62/379,115, filed Aug. 24, 2016, and claims priority from European Patent Application EP 16 185 554.9, filed Aug. 24, 2016, the contents of which are hereby incorporated by reference in their entirety.

BACKGROUND Field

The present invention relates to a polyaxial bone anchoring device and to a system of an instrument and a polyaxial bone anchoring device. The polyaxial bone anchoring device comprises a receiving part for coupling a rod to a bone anchoring element and a clamping ring. The receiving part has a flexible head receiving portion and the clamping ring is configured to be arranged around the head receiving portion. When the clamping ring is around the head receiving portion, the clamping ring can assume a locking position wherein the clamping ring exerts a force onto the head receiving portion such that an inserted head is locked, and a non-locking position wherein an inserted head is pivotable relative to the receiving part.

Description of Related Art

US 2013/0085536 A1 describes a polyaxial bone anchoring device including a receiving part with a rod receiving portion and a head receiving portion for introducing and clamping of the head of a bone anchoring element and a locking ring configured to be arranged around the head receiving portion. The locking ring includes an engagement structure in the form of circumferentially extending ribs for engagement with a tool to allow the locking ring to be moved out of the locking position, i.e. releasing the locking mechanism. This enables a surgeon or other practitioner to carry out revisions or further positioning or re-positioning of the angular position of a receiving part with respect to the bone anchoring element.

US 2011/0060374 A1 describes a percutaneous access device which includes an inner tube and an outer tube and also describes a bone anchor having a distal bone engaging portion and a receiving member having a recess for receiving a spinal fixation element. The proximal end of the receiving member may have an arcuate groove formed on an exterior surface thereof to facilitate connection of an instrument to the receiving member.

SUMMARY

Embodiments of the invention provide a polyaxial bone anchoring device that allows an improved handling during surgery, and provide a system including an instrument adapted for use with such a polyaxial bone anchoring device.

According to embodiments of the invention, a receiving part of a polyaxial bone anchoring device comprises a first engagement structure configured to be engaged by a corresponding engagement portion of an instrument, wherein the first engagement structure is positioned on an outer surface of the receiving part directly at or adjacent to an end surface of a top end of the receiving part. The end surface may for example be an annular end surface of a leg of the receiving part formed by a rod receiving channel. The positioning of the engagement structure directly at or adjacent the first end allows to easily find a receiving part and an aligned attachment position for an instrument in an incision or hole formed in a tissue of a human body.

Due to such an arrangement of the first engagement structure, the receiving part may be engaged by an instrument at a position more distant away from an implant site in the bone and closer to the operator. Accordingly, a need for sufficient space for the receiving part and instrument within an incision or hole formed in the tissue of the human body may be reduced. In other words, less body tissue may be affected by removal when creating the incision and a visual control of operation steps during surgery may be improved. If the engagement structure is formed as a rib circumferentially extending along the end face, the instrument having a corresponding circumferential notch may be applied to the receiving part with an easy find and rotation process.

The polyaxial anchoring device may further comprise a clamping ring, which, when moved relative to the receiving part in an axial direction, locks or unlocks the head of an anchoring element received in the receiving part. In such an embodiment, there may further be provided a second engagement structure arranged at upwardly projecting arms provided at the clamping ring. Due to such arms, even the second engagement structures may be in a position close to the top end and the first engagement portion of the receiving part. An instrument configured to cooperate with the receiving part to effect locking and unlocking of an anchoring element received in the receiving part may be provided with a corresponding engagement portion.

In a further embodiment, a third engagement structure of the receiving part cooperates with a further engagement portion of the instrument. The further engagement portion includes an abutment mechanism (a stop) and optionally a self-locking mechanism. The abutment mechanism is realized by an abutment face which serves as an endpoint of an engaging movement, while the self-locking mechanism may be realized by an inclined section of a guiding wall portion of the further engagement portion of the instrument which creates an increasing amount of friction during engagement by the third engagement portion.

The abutment mechanism allows to establish a correct alignment between the instrument and the polyaxial bone anchoring device while the self-locking mechanism advantageously allows to maintain and control the locked engaged position and to avoid unintentional disengagement.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will become apparent from the description of embodiments by means of the accompanying drawings. In the drawings:

FIG. 1 shows an exploded perspective view of an embodiment of a polyaxial bone anchoring device according to the invention;

FIG. 2 shows a perspective view of the polyaxial bone anchoring device of FIG. 1 in an assembled state;

FIG. 3a shows a perspective view from the top of a receiving part of FIG. 1;

FIG. 3b shows a perspective view from the bottom of the receiving part of FIG. 1;

FIG. 4a shows a cross-sectional view of the receiving part of FIGS. 3a and 3b along a line A-A in FIG. 4 c;

FIG. 4b shows an enlarged view of the head receiving portion of the receiving part of FIG. 4 a;

FIG. 4c shows a top view of the receiving part of FIG. 4 a;

FIG. 4d shows a cross section of an upper part of the receiving part of FIG. 4a in an enlarged view;

FIGS. 5a to 5d show a cross section, a top perspective view, a top view and a bottom perspective view of a clamping ring of FIG. 1;

FIG. 6 shows a perspective view of multiple instruments according to an embodiment of the invention each engaging a polyaxial bone anchoring device according to FIG. 1;

FIG. 7 shows a perspective view of the instrument according to the embodiment and the polyaxial bone anchoring device in an engaged state;

FIGS. 8a to 8b show perspective views from the top and the bottom of the instrument of FIG. 7;

FIGS. 9a to 9b show cross sectional views of the instrument of FIG. 7 in two different views perpendicular to each other.

FIG. 10 shows an enlarged perspective view of a front end portion of the instrument of FIG. 7;

FIG. 11 shows a view onto the front end portion of FIG. 10 along a central axis of the instrument of FIG. 7;

FIG. 12 shows a side view of the inner wall surface of one of the legs of the front end portion of the instrument;

FIGS. 13a to 13d show steps of engaging the polyaxial bone anchoring device using the instrument of FIG. 7;

FIGS. 14a to 14b show cross sectional views of the instrument and polyaxial bone anchoring device in an engaged state;

FIG. 15 shows an enlarged view of engagement portions and structures of the instrument and the polyaxial bone anchoring device in an engaged state, respectively;

FIG. 16a shows a side view of the instrument and the polyaxial bone anchoring device in an engaged state;

FIG. 16b shows a horizontal cross sectional view taken along line B-B in FIG. 16 a;

FIG. 16c shows a horizontal cross sectional view taken along line C-C in FIG. 16 a;

FIGS. 17a to 17c show alternative embodiments of engagement structures at a receiving part.

DETAILED DESCRIPTION

As shown in FIGS. 1 and 2, a bone anchoring device according to an embodiment of the invention includes a bone anchoring element 1 in the form of, for example, a bone screw having a shank 2 with a threaded portion and a head 3 with a spherically-shaped outer surface portion. The head 3 may have a recess 4 for engagement with a driver or tool. The bone anchoring device also includes a receiving part 5 for receiving a rod 6 to be connected to the bone anchoring element 1. Further, a pressure member 7 may be provided in the receiving part 5 for exerting pressure onto the head 3 of the bone anchoring element 1. In addition, the bone anchoring device includes a clamping ring 8 that is mountable to the receiving part 5 for compressing a portion of the receiving part 5 to exert pressure onto the pressure member 7 and in turn onto the head 3. Lastly, the bone anchoring element also includes a fixation element 9 in the form of, for example, an inner screw or set screw for fixing the rod 6 in the receiving part 5.

The receiving part 5 will be described in greater detail referring additionally to FIGS. 3a to 4d . The receiving part 5 includes first end 5 a and an opposite second end 5 b and a central axis C that passes through the first end 5 a and the second end 5 b. The first end 5 a may serve as an abutment for a portion of the instrument as described in greater detail below. A passage 51 extends through the receiving part 5 from the first end 5 a to the second end 5 b. The passage 51 may be formed as a cylindrical coaxial bore 51 a in a region from the first end 5 a to a distance from the first end 5 a and may in this embodiment narrow into an accommodation space 51 b with an inner diameter that decreases towards the second end 5 b until a region with a minimum diameter is reached. The accommodation space 51 b serves for accommodating head 3 of the bone anchoring element 1 and at least a portion of the pressure member 7, as can be seen also in FIGS. 14a, 14b . Adjacent the second end 5 b, a tapered or more specifically conically shaped bottom opening portion 51 c extends from the region having the minimum diameter.

A substantially U-shaped recess 52 extends from the first end 5 a in a direction of the second end 9 b wherein a width of the recess 52 is slightly larger than a diameter of the rod 6, such that the rod 6 can be placed in the recess 52 and can be guided therein. The recess 52 forms a channel for the rod 6. By means of the recess 52, two free legs 52 a, 52 b are formed, on which an internal thread 53 may be provided. In this embodiment, the internal thread 53 extends from an annular end surface 10 defined by first end 5 a up to a distance from the first end 5 a inside the bore 51. The internal thread 53 can be, for example, a metric thread, a flat thread, a negative angle-thread, a saw-tooth thread or any other thread form. Meanwhile, the fixation element 9 in the form of an inner screw has a thread corresponding to the internal thread 53 provided on the legs 52 a, 52 b. Preferably, a thread form such as a flat thread or a negative angle thread is used to prevent or reduce the splaying of the legs 52 a, 52 b when the fixation element 9 is screwed-in. An undercut 59 is formed adjacent to internal thread 53 in a direction away from the first end 5 a, as can be seen in FIG. 4 a.

An upper part 50 of the receiving part 5 which is adjacent to the first end 5 a has a substantially cylindrical outer surface except for example two flat recessed portions 56 a, 56 b, etc., which will be explained in more detail below. Also, at the outer surface of the upper part 50 of the receiving part 5, a first engagement structure for engagement with the instrument is provided, wherein the first engagement structure may be formed by two circumferential ribs 54 a, 54 b which are formed on each leg 52 a, 52 b in the embodiment shown, respectively. The ribs 54 a, 54 b are positioned between the top end 5 a and a lower end 50 a of the upper portion 50. Each of the ribs 54 a, 54 b extends over a segment of the circumference of the upper portion 50, for example, for approximately a quarter circle or less, for example by an angle of about 60° (see FIG. 4c ) as in the embodiment shown. The arrangement is such that one end 540 a 1, 540 b 1 of each rib 54 a, 54 b is positioned at the recess 52 and the other end 540 a 2, 540 b 2 of each rib extends approximately to the middle section of each leg 54 a, 54 b as seen in a circumferential direction. Hence, in a circumferential direction, there is a rib-free surface portion 55 a, 55 b on the outer surface of each leg 52 a, 52 b which extends in that direction between the respective other end 540 a 2, 540 b 2 of the rib 54 a, 54 b and a respective other edge of U-shaped recess 52.

Furthermore, the ribs 54 a, 54 b are arranged in an asymmetric manner with respect to a plane extending through the central axis C of the coaxial bore 51 and a longitudinal axis L of the recess 52. More specifically, the position of the ribs 54 a, 54 b is offset by 180° measured in relation to the central axis C and is rotated with respect to the central axis C such that the rib 54 a of the leg 52 a extends to the rod receiving recess 52 at one side of the receiving part 5 and the rib 54 b extends to the rod receiving recess 52 at the other side of the receiving part 5. This permits the instrument to be placed first onto the rib-free portions 55 a, 55 b and then to be rotated to engage the ribs 54 a, 54 b as described in greater detail below.

The ribs 54 a, 54 b may have a substantially rectangular cross-section or any other shape, but as can be seen in FIGS. 4a and 4d , a dovetail-shape which in this embodiment is single-sided is preferable. Namely, the ribs 54 a, 54 b include a horizontal upper surface 141 which extends substantially perpendicular to the central axis C, while a bottom surface 142 is inclined and extends radially downwards, i.e., towards the distal direction. In other words, a width of the ribs 54 a, 54 b increases in a direction radially outwards (as seen from the central axis C) allowing for a more stable and reliable connection with the instrument when a corresponding complementary profile is also provided therein. The horizontal upper surface 141 in this embodiment is flush with the annular end surface 10 of the legs 52 a, 52 b of the receiving part 5 which is provided at the first end 5 a. Nevertheless, in an alternative embodiment illustrated in FIG. 17a , ribs 54′ of modified receiving part 5′ may also have a full two-sided dovetail-shape. The annular end surface 10 needs not to be planar. It may have an inclination directed inwards or outwards, or may be rounded. In preferred embodiments, the upper surface of the ribs 54 a, 54 b, 54′ forming the first engagement structure is continuous with the annular end surface 10.

In any case, the ribs 54 a, 54 b and 54′ in these embodiments are arranged directly at the annular end surface 10 of the legs 52 a, 52 b defined by the first end 5 a of the receiving part 5, 5′ or at least adjacent to that annular end surface 10 at first end 5 a. Protrusions or recesses formed in the annular end surface are not ruled out, as long as the annular end surface 10 at first end 5 a may serve as an abutment surface for the instrument as described below. A distance of the upper surface 141 of the ribs 54 a, 54 b from the annular end surface 10 of less than a width of the ribs in a direction parallel to the central axis C may be acceptable and is covered by the term “adjacent”.

An advantage of the arrangement of ribs 54 a, 54 b at the top of the receiving part 5 directly at or adjacent to an annular end surface 10 at the first end 5 a arises from the fact that the engagement features of the bone anchoring device are positioned away from the bone surface when the anchoring element is implanted within the bone and the head of the anchoring element is received in the accommodation space of the receiving part. This in turn allows that the instrument engages the device remote from the bone surface which avoids damages to the body tissue and permits to create small incisions. Also, this structure of the receiving part allows the engaging instrument to be configured more stable and sustainable, which will become clear from explanations with regard to the instrument below.

It is noted that the ribs may also have a substantially rectangular, trapezoidal, rhomboid-shaped, tooth-shaped or rounded cross-section, etc., or with regard to further modified receiving parts 5″, 5′″, the ribs 54″, 54′″ may even have complex shapes as illustrated in FIG. 17b or 17 c, respectively. The ribs 54 a, 54 b may have inclined or rounded end portions. It shall be understood that a number of ribs is not limited to just one per leg 52 a, 52 b. More ribs may be implemented below the ribs 54 a, 54 b, such as stop ribs 54 a′, 54 b′ as examples of third engagement structures.

Stop ribs 54 a′, 54 b′ have a length less than that of the ribs 54 a, 54 b as can be seen in FIGS. 3a, 3b . Nevertheless, similar to ribs 54 a, 54 b, stop ribs 54 a′, 54 b′ extend from the rod receiving recess 52 at respective sides of the receiving part 5, and also extend in a distance and parallel to ribs 54 a, 54 b in a circumferential direction on the cylindrical outer surface of upper part 5. The cross section of stop ribs 54 a′, 54 b′ is in this embodiment rectangular as can be seen in FIG. 4a , but the same shapes as detailed with regard to ribs 54 a, 54 b are possible as well. Stop ribs 54 a′, 54 b′ may also include rounded and/or inclined end portions. The width may be equal to or less than that of ribs 54 a, 54 b, or may even be larger. In this embodiment, the width of stop ribs 54 a′, 54 b′ is smaller than that of ribs 54 a, 54 b. The stop ribs 54 a′, 54 b′ are arranged directly at or adjacent to an upper end wall 561 of recessed surface portions 56 a, 56 b.

As noted, the outer surface of the receiving part 5 also includes the substantially flat or planar recessed portions 56 a, 56 b. Recessed portions 56 a, 56 b are positioned at the upper part 50 in a circumferential direction in correspondence with the circumferentially extending ribs 54 a, 54 b and extend from an edge 50 a at a bottom end of upper part 50 in a proximal direction parallel to the central axis C up to a predetermined distance from the ribs 54 a, 54 b. The recessed portions 56 a, 56 b need not have a planar flat surface recessed from a cylindrical outer contour of the receiving part 5 as in the embodiment but may also be rounded and/or provided with side walls. The recessed portions 56 a, 56 b serve as a guiding surface for upwardly projecting arms 83 a, 83 b of clamping ring 8 as will be detailed below.

Between the upper part 50 and the second end 5 b of the receiving part 5 a head receiving portion 57 of the receiving part 5 is provided that includes the accommodation space 51 b. The head receiving portion 57 also has a substantially cylindrical outer surface that has a smaller diameter than the diameter of the upper part 50 of the receiving part 5. Adjacent the second end 5 b, there is a portion 57 a of the outer surface that slightly tapers outwards. To allow insertion of the head 3, the head receiving portion 57 is flexible. In the embodiment shown, the head receiving portion 57 includes a plurality of flexible wall sections 57 b that are separated by slits 58 extending in a longitudinal direction and being open towards the second end 5 b. According to embodiments, the slits 58 may or may not extend even up into the upper part 50 of receiving part 5, as can be seen in FIGS. 3a and 3b . The number and size of the slits 58 is provided depending on the desired flexibility of the head receiving portion 57.

An inner diameter of the passage 51 at the second end 5 b is smaller than a diameter of the head 3 of anchoring element 1. Due to the flexibility of the head receiving portion 57 the head 3 could be inserted from the second end 5 b, but with the clamping ring 8 arranged in place embracing the head receiving portion 57, there is not sufficient expansion of the flexible wall sections 57 b to allow insertion from the bottom end. In use, the anchoring element 1 in this embodiment will rather be inserted into the receiving part 5 via first end 5 a (i.e., top loading).

The clamping ring 8 will be described in greater detail referring additionally to FIGS. 5a to 5 d.

The clamping ring 8 comprises an upper end or first end 8 a and an opposite lower end or second end 8 b and may have a substantially spherical outer surface 81 which narrows towards the second end 8 b. The outer diameter of the spherical surface 81 at or adjacent the first end 8 a may be such that when the clamping ring 8 is mounted around the head receiving portion 57 of the receiving part 5, the outer spherical surface 81 of the clamping ring and the outer cylindrical surface of the upper part 50 of the receiving part 5 are flush with each other as depicted, for example, in FIG. 2. An inner diameter of the clamping ring 8 is such that the clamping ring 8 can be mounted around the head receiving portion 57 wherein the upper end 8 a faces towards the bottom end or edge 50 a of the upper part 50 of the receiving part 5. Alignment features in the form of flat portions 82 are provided at the outer surface 81 of the clamping ring 8. The flat portions 82 are offset by 180°. The alignment features may assist in aligning the clamping ring 8 correctly with respect to the receiving part 5, in particular with respect to further flat surfaces 50 b recessed from the cylindrical outer surface of upper part 50 directly below the U-shaped recess 52, see FIG. 3a . It shall be noted, however, that the shape of the outer surface of clamping ring 8 may be different in other embodiments. For example, the outer surface 81 may have a cylindrical shape etc.

As can be seen in particular in FIG. 5a , clamping ring 8 further has a first inner cylindrical surface portion 86 that is adjacent or substantially adjacent to the upper end 8 a. There may be a small inclined surface or beveled surface (not shown) provided adjacent to the upper end 8 a to facilitate mounting. Adjacent or substantially adjacent to the lower end 8 b, a second inner surface portion 87 of the clamping ring 8 may be tapered in such a manner that the inner diameter conically widens towards the lower end 8 b. The second inner surface portion 87 is configured to cooperate with the outer surface portion 57 a of the head receiving portion in such a manner that when the clamping ring 8 is moved towards a lowermost position on the head receiving portion 57, the cooperating surfaces 57 a of the head receiving portion 57 and 87 of the clamping ring 8 exert an increasing inwardly directed radial force towards the head 3. Moreover, a height of the ring-shaped base portion (between ends 8 a, 8 b, i.e., without arms 83 a, 83 b) of clamping ring 8 in an axial direction, as can be seen in FIGS. 14a and 14b , corresponds substantially to a height of the head receiving portion 57 of the receiving part 5.

The clamping ring 8 includes two upwardly projecting arms 83 a, 83 b extending from a shoulder 85 formed at first end 8 a. As can be seen particularly in FIGS. 2, 14 a and 14 b, the length of arms 83 a, 83 b substantially corresponds to a length of recessed portions 56 a, 56 b (as measured from the edge 50 a at the bottom end of upper part 50) in a direction parallel to the central axis C, which are arranged to slideably receive arms 83 a, 83 b, when the clamping ring 8 is attached to the receiving part. Each of arms 83 a, 83 b has end faces 89 which may abut on—or at least may approach close to—upper end wall 561 of the recessed portions 56 a, 56 b. Similarly, the width of arms 83 a, 83 b substantially corresponds to that of recessed portions 56 a, 56 b. The two arms 83 a, 83 b are located diametrically opposite to each other and are positioned asymmetrically with respect to the flat portions 82. More specifically, the position of both arms 83 a, 83 b is rotated in the same direction by for example about 60° in this non-limiting embodiment with respect to flat portions 82 in the circumferential direction, which is indicated in FIG. 5c by the dash-dotted axis R that will be aligned with longitudinal axis L of the U-shaped recess 52 in an assembled state.

Each of the two upwardly projecting arms 83 a, 83 b includes an engagement structure for engagement with an instrument on its outer surface within or adjacent a tip portion of the respective arm which in this embodiment is provided as a dovetail-shaped circumferentially extending engagement structure formed as a notch 88 a, 88 b. As already noted above a consequence of such positioning at a tip portion of the arms 83 a, 83 b, the engagement structure of the clamping ring 8 as well as the engagement structure of the receiving part are located (i) close to each other and (ii) at a portion of a respective piece most proximate to the first end 5 a of the receiving part 5 and away from the head receiving portion 57, i.e., away from the bone surface when the polyaxial bone anchoring device is in an assembled state in-situ. This allows to require less space within the body tissue by an instrument for performing steps of intermittent locking/unlocking during, e.g., repositioning of single vertebra or readjusting of a receiving part with an unlocked rod, wherein the clamping ring 8 is engaged and axially displaced by for example an outer tube of a locking/unlocking instrument with respect to an inner tube of the locking/unlocking instrument, which engages the receiving part 5. Examples of a similar instrument that can be used for locking and releasing a lock on a bone anchoring device, and similar interactions of such an instrument with other bone anchoring devices, are disclosed in U.S. Provisional Patent Application Ser. No. 62/371,029 and European Patent Application EP 16 182 818.1, the contents of which are hereby incorporated by reference in their entirety.

According to embodiments of the invention, the arms 83 a, 83 b have a sufficient length that the engagement structures provided on the arms, such as notches 88 a, 88 b, are arranged at an axial position in the direction of the central axis C corresponding to that of the rod 6 when the rod is received in the U-shaped recess 52 and pressed against the pressure member 7 (i.e., in a locked state of the bone anchoring device), preferably even at or above an axial position of a largest diameter of the rod 6 like in the embodiment illustrated herein, see FIGS. 14a , 14 b.

In compliance with the dovetail-shaped cross sectional profile, a width of notches 88 a, 88 b decreases in a direction radially outwards towards the outer surface of arms 83 b. The notches 88 a, 88 b include a cylindrical base surface 880 coaxial with the central axis C and correspondingly inclined bottom surfaces 881 and upper surfaces 882 as can be seen in more detail in FIG. 5a . It is noted that the engagement structure provided at the arms 83 a, 83 b need not be a notch 88 a, 88 b but may also be provided as a protruding rib as in the case of ribs 54 a, 54 b. Also, the cross sectional profile of the engagement structure formed as notches 88 a, 88 b or ribs may be substantially rectangular, trapezoidal, rhomboid-shaped, tooth-shaped or rounded, etc. instead of being dovetail-shaped.

A length of the engagement structures, e.g., notches 88 a, 88 b, is limited to the width of the arms 83 a, 83 b and substantially corresponds to that of the engagement structures of the receiving part, i.e., the circumferential ribs 54 a, 54 b. A depth of the recessed portions 56 a, 56 b and a thickness of the arms measured in radial direction is defined such that the cylindrical base surface 880 of notches 88 a, 88 b is substantially flush with the cylindrical outer surface of the receiving part 5, when the clamping ring is assembled with the receiving part. As a consequence, a dovetail-shaped circumferentially extending rib as an example of an engagement portion in an outer tube of the locking/unlocking instrument may be smoothly slid into a corresponding notch 88 a, 88 b of the clamping ring 8. However, a small step between the cylindrical outer surface of the receiving part 5 and base surface 880 of the notches 88 a, 88 b is not ruled out. Furthermore, it is not ruled out that further notches or ribs are provided at arms 83 a, 83 b.

The pressure member 7 as shown in FIGS. 1 and 14 a, 14 b comprises a substantially cylindrical outer surface 71 which has a diameter that is equal to or slightly smaller than an inner diameter of the cylindrical coaxial bore 51 a to facilitate sliding and accommodation therein. Pressure member 7 also has a rod receiving portion 72 which is cylinder-segment shaped for receiving a rod 6 therein and which forms two legs opposite each other, which face the first end of the receiving part when the pressure member 7 is inserted in the coaxial bore 51 a. Moreover, a spherical hollow section 73 is formed at a lower end of pressure member 7 which contacts the head 3 of anchoring element 1 and may exert pressure transferred from an inserted rod 6 onto the head 3 to lock the same when for example fixation element 9 is tightened. The pressure member may further comprise a coaxial hole allowing access to recess 4 which is provided in the head 3 of anchoring element 1.

The receiving part 5, the clamping ring 8, the pressure member 7, the fixation element 9 and the bone anchoring element 1 may be made of bio-compatible materials, for example of titanium or stainless steel, of a bio-compatible alloy, such as a NiTi-alloys, for example Nitinol, magnesium or magnesium alloys or from a bio-compatible plastic material, such as, for example, polyether ether ketone (PEEK) or poly-l-lactide acid (PLLA). The parts can be made of the same or of different materials.

In operation, the polyaxial bone anchoring device 100 is first assembled by attaching the clamping ring 8 to the flexible head receiving portion 57 via the second end 5 b, wherein the flexible wall sections 57 b are slightly compressed by the first and second inner surface portions 86, 87 of the clamping ring 8. Also, the bone anchoring element 1 is inserted into the receiving part 5 via the first end 5 a. The pressure member 7 may then also be slid into the coaxial bore 51 a of receiving part 5, and the anchoring element 1 is applied to a bone using, e.g., a driver or tool. A rod 6 may then be guided into the U-shaped recess 52 of receiving part 5 and using a locking/unlocking instrument the clamping ring is axially moved in the distal direction away from the first end 5 a towards a lowermost position on the head receiving portion 57 to clamp the head 3, wherein the conical second inner surface portion 87 of clamping ring 8 cooperates with the outer surface portion 57 a of the head receiving portion in such a manner that an increasing inwardly directed radial force is exerted towards and onto the head 3.

Thereby, the fixation element 9 needs not to be tightened yet. Rather, a locking/unlocking instrument allows a temporary clamping and/or unclamping via the actuating, i.e., moving clamping ring between a clamping position and a pre-locking position. This function permits the operator to readjust and fix an angular position of the receiving part with respect to the anchoring element even without an inserted rod, or to reposition individual vertebrae via the attached instrument. Nevertheless, final fixation will be effected by tightening the fixation element 9 and thus pressing the pressure member 7 against the head 3 to lock the same.

Next, an instrument 200 for use with the polyaxial bone anchoring device 100 will be explained with reference to FIGS. 6-12. The instrument 200 functions as a head extension device which is configured to be attached to the receiving part 5 in-situ and thereby allows manipulating the receiving part 5 or supplying further instruments and/or parts to the receiving part 5. Multiple such instruments 200 may be attached to respective polyaxial bone anchoring devices 100 in-situ as illustrated in FIG. 6, the polyaxial bone anchoring devices 100 being positioned within vertebrae, respectively. Unlike the above explained instrument for locking/unlocking the clamping ring 8, which also engages the clamping ring 8 in addition to the receiving part 5, the instrument 200 is arranged to only engage the ribs 54 a, 54 b at the receiving part. Nevertheless, embodiments of any instruments such as the above described locking/unlocking instrument that are also configured to engage receiving part 5 of polyaxial bone anchoring device 100 disclosed herein are encompassed by the appended claims.

The instrument 200 includes a tubular member 202 having a front end portion 204, which comprises engagement portions for engagement with the engagement structures of the receiving part, and a rear end portion 206 as can be seen in FIG. 7.

As shown in FIGS. 8a-9b , the tubular member 202 includes an inner bore 212 extending from the rear end portion 206 to the front end portion 204, and the front end portion 204 is provided with a substantially rectangular-shaped recess 214 into which the bore 212 opens, and which forms two free legs 214 a, 214 b. The inner bore 212 has a diameter smaller than that of the receiving part 5. Inner bore 212 ends at an annular abutment surface 217, which serves to abut on annular end surface 10 of receiving part 5 during engagement. The tubular member 202 further has recessed portions 210 at opposite sides thereof in a region of the rear end portion 206, which may serve for attaching further instruments or for gripping the instrument.

As can be seen in FIG. 10, the legs 214 a, 214 b each includes a rounded tip portion 215 a, 215 b, respectively, which facilitates insertion of the instrument into the incision or hole in the tissue and guiding to the in-situ position of the receiving part 5. A length of the rounded tip portion 215 a, 215 b in a direction of a central axis T of the instrument is small compared to the portion of the free legs which has a substantially cylindrical contour and constant width measured in a radial direction from the central bore 212.

At an inner surface of the instrument in a region of the tip portion 215 a, 215 b of the free legs of the frond end portion 214 there are provided two engagement portions in the form of notches 216 a, 216 b. These notches 216 a, 216 b have a single-sided dove-tail-shaped cross section, which is complementary to that of the ribs 54 a, 54 b provided at the receiving part 5. Notches 216 a, 216 b are configured to slideably receive the ribs 54 a, 54 b during engagement by rotation in a circumferential direction as will be detailed below. Notches 216 a, 216 b extend between the recess walls and open into the recess 214 on both sides thereof in the circumferential direction around central axis T and have a length which corresponds to that of ribs 54 a, 54 b, covering for example an angle of 45°. As with regard to ribs 54 a, 54 b, the cross section may be different from a (single sided) dovetail-shape. Also the length may vary and depends on the width of the legs 214 a, 214 b.

Moreover, second engagement portions in the form of stop notches 218 a, 218 b are provided directly at the edge of the tip portions 215 a, 215 b extending from the recess at one open end 220 a thereof in a circumferential direction around central axis T. More specifically, the notches 218 a, 218 b have a length shorter than that of notches 216 a, 216 b. As a consequence, stop notches 218 a, 218 b include an end or abutment face 220 b facing in a circumferential direction, in this embodiment facing in the counter-clockwise direction in both cases.

Stop notches 218 a, 218 b are configured to slideably receive stop ribs 54 a′, 54 b′ therein during engagement by rotation in a circumferential direction as will be detailed below. However, as a consequence of the abutment faces 220 b, rotational movement of the instrument 200 with respect to the receiving part 5 is limited by these abutment faces 220 b functioning as a stop. Advantageously, such stop guarantees that the instrument 200 attains a correctly aligned engagement position with respect to the receiving part 5 and does not unintentionally lose contact with the receiving part during use, which otherwise might be harmful for the patient and also might damage the engagement features.

Still further, as can be seen in FIG. 10, the stop notches 218 a, 218 b do no need to have a lower wall. Rather, the notches 218 a, 218 b are also open towards the distal direction, i.e., towards second end 5 b of receiving part 5. Since an axial position of the instrument 200 with respect to the receiving part 5 is already defined by ribs 54 a, 54 b received in notches 216 a, 216 b, the lower walls can be omitted and the stop notches 218 a, 218 b herein merely provide for the stop function. Due to the omission of the lower walls, the tip edge of instrument 200 is further closer to the ribs 54 a, 54 b seen in the axial direction, which further reduces the depth with which the instrument has to enter the incision in order to engage the receiving part. This feature further avoids delicate parts arranged near the tip and the engagement portions which inevitably undergo large lever actions during use.

As can be seen in FIG. 12, the stop notches nevertheless have an upper guiding wall, which, however, has two sections, namely an annular horizontal section 221 which extends in a plane perpendicular to the central axis T, and an inclined section 222. The horizontal section 221 is located extending from the open end 220 a of notches 218 a, 218 b, while the inclined section 222 extends adjacent to horizontal section 221 up to the abutment face 220 b at the other end of notches 218 a, 218 b. The inclination is such that the width of notches 218 a, 218 b narrows towards the abutment end 220 b. As a consequence, during sliding-in of a rib 54 a′, 54 b′ received in one of the notches 218 a, 218 b from the open end 220 a in a rotational movement towards the abutment face 220 b, such rib 54 a′, 54 b′ eventually contacts the inclined surface which in turn creates a frictional force between the rib 54 a′, 54 b′ and the inclined surface 222.

Advantageously, this function on the one hand assists in maintaining an engaged state of the instrument 200 with the receiving part 5 and prevents unintentional loosening. On the other end, the operator obtains a tactile response during the rotational movement of the instrument that he is approaching the stop.

It is noted that between the notches 54 a and 54 a′ as well as between notches 54 b and 54 b′ there extends a cylindrical inner surface 219, which as compared with the inner surface of inner bore 212 has an enlarged diameter, which corresponds to the diameter of the outer cylindrical surface of the upper part 50 of the receiving part 5. This cylindrical inner surface 219 serves for guiding the instrument while placing the instrument on the receiving part 5 as will be explained in the following.

A use of the instrument 200 and the polyaxial bone anchoring device 100 is shown in FIGS. 13a-d . As shown in FIG. 13a the instrument 200 is moved to the receiving part 5 in a direction of the central axes C, T being aligned with each other. Thereby, the free legs 214 a, 214 b are aligned with the rib-free portions 55 a, 55 b of the receiving part 5, respectively, in a circumferential direction.

In FIG. 13b , the instrument 200 is guided over the receiving part 5. The cylindrical inner surface 219 of the instrument 200 slideably contacts the outer cylindrical surface of the upper part of the receiving part 5 and crosses the rib-free portions 55 a, 55 b.

In FIG. 13c , the downward movement of the instrument 200 stops wherein the annular abutment surface 217 at the end of bore 212 abuts on the annular end surface 10 of the receiving part. The rounded tip portion 215 a, 215 b having the engagement portions arranged at its inner wall is in this situation located at an axial position of the engagement structures 54 a, 54 b, 54 a′, 54 b′.

In FIG. 13d , the instrument 200 is rotated in the circumferential direction as indicated by the arrow. Thereby, the ribs 54 a, 54 b of the receiving part 5 slide with leading end portions 540 a 2, 540 b 2 into the respective notches 216 a, 216 b of the instrument 200, and the ribs 54 a′, 54 b′ slide with leading end portions 540 a 2′, 540 b 2′ into the respective notches 218 a, 218 b of the instrument 200. Initially, the inclined surface 222 has contacted an upper surface of ribs 54 a′, 54 b′ creating an increasing friction and slight tension between the ribs 54 a and 54 a′ as well as 54 b and 54 b′. Finally, leading end portions 540 a 2′, 540 b 2′ of each of ribs 54 a′, 54 b′ abuts on respective abutment faces 220 b. The increasing friction thereby leads to self-locking of the engagement between the receiving part 5 and the instrument, whereby the abutment serves to define an aligned endpoint of the rotational movement.

In this final engagement position, which is also shown in FIGS. 14a and 14b , the operator may perform desired steps of assembling and orienting the polyaxial bone anchoring device. FIG. 15 shows an enlarged detail of the engagement structures and portions. FIGS. 16b and 16c reveal horizontal cross sections in the engaged position.

Various modifications may be made without departing from the scope defined by the appended claims. For example, as noted above, the instrument may be different from the head extension instrument and may for example be a locking/unlocking instrument.

Moreover, the polyaxial bone anchoring device may include a pressure member formed as an inner cap itself having a flexible head receiving portion as described for example in European Patent Application EP 16 182 818.1, wherein a head of an anchoring element may be loaded to a head receiving portion of a receiving part from the bottom. In that case, the ribs disclosed therein for example in FIG. 3 are replaced with an arrangement of ribs as explained above while all other features are maintained.

However, it may also be conceived to add arms 83 a, 83 b as described above to the clamping ring disclosed in European Patent Application EP 16 182 818.1 to bring the ribs of the clamping ring and the receiving part into closer proximity like in the embodiment presented above.

While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is instead intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof. 

1. A bone anchoring device comprising: a receiving part for coupling a rod to a bone anchoring element, the receiving part comprising a first end, a second end, a central axis extending between the first end and the second end, an end surface at the first end that faces away from the second end, a recess at the first end for receiving the rod, and a head receiving portion at the second end for pivotably holding a head of the bone anchoring element, the head receiving portion being at least partially flexible; and a clamping ring positionable around the head receiving portion, wherein when the clamping ring is around the head receiving portion, the clamping ring is movable from a first position wherein an inserted head is pivotable relative to the receiving part, to a second position wherein the clamping ring exerts a radial force onto the head receiving portion to lock the inserted head relative to the receiving part; wherein the receiving part further comprises a first engagement structure configured to be engaged by an instrument, wherein the first engagement structure is positioned at or adjacent to the end surface at the first end and extends radially outwardly from an outer surface of the receiving part.
 2. The bone anchoring device of claim 1, wherein the clamping ring comprises a second engagement structure configured to be engaged by the instrument to facilitate axial displacement of the clamping ring relative to the receiving part.
 3. The bone anchoring device of claim 2, wherein the clamping ring comprises an upwardly projecting arm, and wherein the second engagement structure is at the upwardly projecting arm.
 4. The bone anchoring device of claim 3, wherein the second engagement structure is at a region of a free end of the upwardly projecting arm, and wherein the upwardly projecting arm has a length such that the second engagement structure is positioned in a direction along the central axis that is at or above a position of the rod when the rod is held in the recess of the receiving part.
 5. The bone anchoring device of claim 4, wherein the receiving part further comprises a recessed portion extending axially up to a distance from the first end of the receiving part for accommodating the upwardly projecting arm of the clamping ring.
 6. The bone anchoring device of claim 1, wherein the clamping ring comprises an upwardly projecting arm.
 7. The bone anchoring device of claim 1, wherein at least one surface of the first engagement structure has a dovetail-shaped cross-section.
 8. The bone anchoring device of claim 1, wherein the first engagement structure extends farther radially outwardly than all other portions of the receiving part.
 9. The bone anchoring device of claim 1, wherein a surface of the first engagement structure that faces away from the second end of the receiving part is flush with the end surface at the first end of the receiving part.
 10. The bone anchoring device of claim 1, wherein the end surface at the first end of the receiving part forms an annular-segment shaped end surface of legs formed by the recess.
 11. The bone anchoring device of claim 1, further comprising a pressure member positionable in the receiving part and configured to exert pressure on the head when the head is held in the head receiving portion of the receiving part.
 12. The bone anchoring device of claim 1, wherein the first engagement structure is arranged asymmetric with respect to a plane extending through the central axis of the receiving part and through a longitudinal axis of the recess.
 13. The bone anchoring device of claim 1, wherein the receiving part further comprises a third engagement structure which is aligned with the first engagement structure in the circumferential direction and is spaced apart axially from the first engagement structure, and wherein the third engagement structure comprises a circumferentially facing abutment end.
 14. A system comprising the bone anchoring device of claim 13 and an instrument comprising at least one tubular member comprising: a first engagement portion formed as a notch for engaging the first engagement structure at the receiving part; and a second engagement portion for engaging the third engagement structure at the receiving part, wherein the second engagement portion comprises an abutment face for facing and abutting against the abutment end of the third engagement structure when the first engagement structure and the first engagement portion are engaged.
 15. The system of claim 14, wherein the second engagement portion of the instrument further comprises a guiding wall with an inclined section with respect to the circumferential direction to provide a self-locking mechanism.
 16. A system comprising the bone anchoring device of claim 1 and an instrument comprising at least one tubular member comprising a first engagement portion formed as a notch for engaging the first engagement structure at the receiving part.
 17. The system of claim 16, wherein the first engagement structure is configured to be engaged by the instrument via a rotational movement of at least part of the instrument in a circumferential direction around the central axis. 18-19. (canceled)
 20. A bone anchoring device comprising: a receiving part for coupling a rod to a bone anchoring element, the receiving part comprising a first end, a second end below the first end, a central axis extending between the first end and the second end, an end surface at the first end that faces away from the second end, a recess at the first end for receiving the rod, and a head receiving portion at the second end for pivotably holding a head of the bone anchoring element, the head receiving portion being at least partially flexible; a pressure member positionable in the receiving part and configured to exert pressure on the head when the head is held in the head receiving portion of the receiving part; and a clamping ring positionable around the head receiving portion, wherein when the clamping ring is around the head receiving portion, the clamping ring is movable from a first position wherein an inserted head is pivotable relative to the receiving part, to a second position wherein the clamping ring exerts a radial force onto the head receiving portion to lock the inserted head relative to the receiving part; wherein the receiving part further comprises a first engagement structure configured to be engaged by an instrument, wherein the first engagement structure is positioned at or adjacent to the end surface at the first end and extends radially outwardly from an outer surface of the receiving part.
 21. A bone anchoring device comprising: a receiving part for coupling a rod to a bone anchoring element, the receiving part comprising a first end, a second end, a central axis extending between the first end and the second end, an end surface at the first end that faces away from the second end, a recess at the first end for receiving the rod, and a head receiving portion at the second end for pivotably holding a head of the bone anchoring element, the head receiving portion being at least partially flexible; and a clamping ring positionable around the head receiving portion, wherein when the clamping ring is around the head receiving portion, the clamping ring is movable from a first position wherein an inserted head is pivotable relative to the receiving part, to a second position wherein the clamping ring exerts a radial force onto the head receiving portion to lock the inserted head relative to the receiving part; wherein the receiving part further comprises an outer surface at the first end, the outer surface extending circumferentially around the central axis at a first radial distance from the central axis, and a first engagement structure that extends radially outwardly from the outer surface for engagement with an instrument, wherein the first engagement structure is positioned at or adjacent to the end surface at the first end. 